1. Field of the Invention
This invention relates to a multi-cavity high pressure injection molding system and method of operation thereof where the cavity or cavities that are first to fill cavities each have an overflow cavity connected thereto, the overflow cavity being adjustable in size without removing the overflow cavity from the molding system.
2. Description of the Prior Art
It is known to have family molds having multi-cavities used to make different components of the same part simultaneously. It has been recognized with family molds that it is important to balance the mold system so that all of the cavities fill at approximately the same time with approximately the same pressure. Otherwise, some components will be overpacked while others will be underpacked leading to different shrinkage properties and different performance characteristics of the various components that make up the same part. For example, the plastic from smaller cavities might have a different gloss from plastic in the larger cavities or may be much more brittle or plastic obtained from larger cavities may have sinking on the surface. It is desirable that the cavities are controlled so that the pressure within each cavity and the time to fill each cavity is approximately the same.
The Maus, et al. U.S. Pat. No. 5,512,221 describes a method and apparatus for making contact lenses where the mold is adjustable. The mold is a low pressure mold and is adjustable to change the thickness of the lens being molded. As can be appreciated, the degree of change is extremely minute and the mold is a single mold and is not part of a molding system. The Hendry U.S. Pat. No. 5,098,637 describes a process for injection molding hollow plastic articles by sequentially injecting fluent plastic and gas into a mold cavity. The Hendry U.S. Pat. No. 5,607,640 describes an injection molding system where the size of a spill cavity varies during the injection of plastic. With the present invention, there is no injection of gas sequentially with the plastic and the overflow cavity has a fixed volume during the molding process.
While automated degating is known, it is carried out by a passageway being machined into the mold steel to reach the cavity. The passageway tapers as the cavity is approached and the material in the passageway is severed from the side wall of the cavity when the material is ejected at the end of the molding process. This type of gate restricts flow and cannot be used effectively for material flow passing from a part cavity to an overflow cavity.